You say your looking for a way to Orgeon? Follow me!
Thank you! 
Oregon Trail
Do we float across?
Manifest Destiny
God had personally told me that we were meant to move westward!
He told me the exact same thing!
Fur trappers that lived in the mountains. Helped people move west through the mountains. Established forts and trails throughout the mountains.
Mexican-American War
Remember the Alamo!
Americans left to move west from Independence, Missouri to follow the Oregon trail, they faced hardships such as death, rivers, mountains, and cliffs, The trail led all of them westward, to where they would end up settling.  
Mormons in Utah
Americans thought that they were superior to everyone else and that it was their destiny to go westward and settle. This helped people by inspiring them to follow the trail, westward.
California Gold Rush
I found that gold first!
Get your own! This is mine.
The war was an effect of America trying to annex Texas, they fought Mexico who thought the land still belonged to them rightfully, America gained more land westward, such as California and New Mexico.
This land belongs to us!
They came under fire by other civilians a lot for their religious beliefs, so they decided to move and settle somewhere else. This place happened to be Utah, Hundreds upon hundreds of other Mormons flocked to the settlement. This helped attract many others west towards the settlement. 
They wouldn't accept us, but we found the perfect place to settle!
When gold in California was found, many settlers flocked west to take advantage of the gold rush. Some found gold and made a fortune, others weren't as lucky. Hundreds of people ended up settling in California, therefore helping it become an official state at the end of the rush.